Why 350 ppm is Obvious.

>One of the most important questions on climate is: what level we need to limit CO2 to avoid tipping points?

We’re at 390 ppm (parts per million) now, rising about 2 per year. It was once thought 550 was ok, then 450. James Hansen has argued that 350 ppm is the only really safe target. This is politically unthinkable, technically very difficult – but it’s true.

There are complicated explanations as to why 350 ppm of CO2 is the appropriate target, and a simple one. Credit to Jim Hansen for the complicated one. (Well, that’s the press release which points to the original paper).